Riding with Stacey Griffith at SoulCycle can be life-changing. It certainly felt like that for Jaclyn Darvas, 32, a senior manager at a pharmaceutical company in New York City. After her father passed away from leukemia, Darvas went to a dark place. "It was the most challenging year of my life," she says. "I lost all motivation." Months later, on Thanksgiving morning, she took her first Stacey class. "She taught me how to get up every morning and work through the tough times on the bike," says Darvas. "Stacey didn't just solve my motivation problem. She transformed my life forever."

Behold the power of the super instructor: a new breed of therapist, cheerleader and, yes, trainer, all in one chiseled package. Not into therapeutic mantras? There's an instructor for everyone. (Most major cities have at least one cult of fitness personality; New York City and Los Angeles boast a dozen each.) Ballet Beautiful's Mary Helen Bowers woos students to a fantasy world where leg warmers and leotards are de rigueur. Tracy Anderson's hip-shaking dance-cardio classes make women feel like Madonna (a former Anderson devotee). David Siik, creator of Equinox's Precision Running class, has turned the "dreadmill" into an endorphin machine. "I arrange my travel schedule around David's classes, because he makes me feel stronger and happier," says Samantha Leigh Hubshman, 30, an actress in L.A. "Once, I went straight from the airport to his class, suitcase in hand, and jumped on the treadmill!"

Naturally, she checked Siik's Twitter feed en route. The explosion of social media has helped lift these trainers to super status: Spin, barre and dance-cardio fans in 2015 can not only take an instructor's class but also download her Spotify playlist, read her inspirational quotes on Facebook, see where she had brunch on Instagram and even text her strong-arm emojis after hours. The better the instructor's social media game, the more obsessive her fan base. "Social media helps instructors sell not only a class but a lifestyle," says Britanny Carter, a fitness industry analyst at market research firm IBIS World.

Whether that lifestyle is ballerina or rock star, the super instructor's rise to power is akin to a religious revival. For acolytes, Griffith, a friend of Deepak Chopra, is a spiritual guru in Saint Laurent high-tops. Her class is "my temple and my church," says Glynis Karp, 49, a senior vice president at Ralph Lauren in New York City.

A kind of fairy dust separates the stars from the so-sos: a unique ability to make exercise an emotional, communal experience. It's something the new breed of plugged-in, stressed-out exercisers crave now more than ever, says Pirkko Markula, Ph.D., professor in socio-cultural studies at the University of Alberta. "In our urbanized society, there's less opportunity to form social bonds," she says. "People work long hours and have no time to get to know people outside of work. Fitness classes can be a way of finding a community."

In the end, sculpting muscles and scorching calories are just a bonus. "I don't go to Stacey to work off the cake I ate last night," says Karp. "I go because I walk out thinking, I can be a better mother, a better wife, a better boss, a better friend. I don't get that level of inspiration from another instructor." —Michelle Ruiz

Stacey Griffith, SoulCycle

Top model Grace Mahary (left), shown with Griffith, is a SoulCycle regular.

The room is dark, the music is turned way, way up, and Stacey Griffith—SoulCycle's ripped, cropped-blonde superstar instructor—is in her element, dancing, shouting motivational one-liners and inspiring a packed class of riders to pedal faster, dig deeper and dream bigger. "Whatever your it is, I want you to get down on it!" she shouts, riffing off the song blasting over the sound system, Kool & the Gang's "Get Down on It."

Not many people could turn the chorus of a disco song into a potentially transformative mantra, but it's all in a day's work for Stacey G, as she's known to her SoulCycle fans, of which there are many: 200-plus per day, more than 1,000 per week, at up to $70 a ride. Her classes sell out in seconds online; her students follow her from the Upper East Side to TriBeCa, and beyond: One L.A.-based disciple flies cross-country to Spin with her twice a month. Last year, Oprah, the ultimate seal of approval for all things awesome and inspirational, brought Griffith on her Life You Want Weekend, in which she led crowds of 15,000 in mock rides from their arena seats.

Why? In a word, charisma. It's the way Griffith moves around the candlelit room, swinging her hips, calling out riders by name and claiming her space like she's on stage. It's the feeling that Griffith believes in you, the rider. And it's those well-timed one-liners. The fact that she doesn't even ride a bike only speaks to her power as a performer and motivator. (After injuring her knee in a ski accident years ago, she began teaching from the floor; another instructor demos the moves.)

Griffith started her fitness career in West Hollywood as a trainer and Spin instructor. Eventually, she moved to the Hamptons, where Elizabeth Cutler, SoulCycle's cofounder, took her class and recruited her as the second hire. "Back then, I taught more from my ego. I would flash my abs. Now I don't teach from that 'try to be like me' place," says Griffith. "People cry in my class every day. I make them feel like it's safe to let their feelings out." —Tatiana Boncompagni

Signature Stacey Moves:

Tap Back On a stationary bike, stand on pedals with hands toward top of handlebars. Engage abs and slowly curl hips back, tapping glutes to back of seat. Release abs and pop back up to start. Continue for 30 seconds to beat of music for duration of song, taking 30-second breaks.

Quick Fire While pedaling, place hands toward bottom of handlebars and drop right elbow toward resistance knob, squeezing right obliques. Repeat on left side. Continue for 30 seconds to beat for duration of song, taking 30-second breaks.

Push-Up Standing or sitting on bike, keep hips back and engage core while bending elbows to lower and raise upper body over handlebars. Continue for 30 seconds to beat for duration of song, taking 30-second breaks.

Climb Standing or sitting on bike, add enough resistance to feel it in glutes and hamstrings. Close eyes and set an intention (to let go of frustration, for example). Pedal until end of song.

Mary Helen Bowers, Ballet Beautiful

Stepping into the sun-bathed Ballet Beautiful studio in New York City's SoHo is like entering a fairy tale. Students happily march up five flights of stairs to reach this castle in the sky, where lithe women in petal-pink leg warmers reign, their hair slicked back in ballerina buns. Satin-trimmed tutus dangle on wrought-iron ballet barres. "I want to create an environment that is positive and transformative," says Mary Helen Bowers, the delicate yet formidable creator.

Bowers, who is pregnant with her second child, is quiet, elegant, calm. In other words, decidedly untrainery. She doesn't play music: The only sound is her melodious voice gently guiding students through precise movements that stretch, lengthen and tone. Bowers's quietly rigorous approach has attracted a client roster that includes scores of models—she's flown to Paris for fashion week annually to help them maintain their runway-ready figures—and actresses like Natalie Portman, whom she pliéd into prima ballerina form for the movie Black Swan.

And then there are the thousands of women across the globe who have signed up for her $39-a-month video-streaming membership to hone their own ballerina bodies. Bowers allows no "negative talk" in her studio—from students or instructors—and encourages clients to think of exercise as a self-reward or treat. "My approach is challenging yet supportive," she says. "Fitness is not just about how you look; it's about how you feel." —Tatiana Boncompagni

Signature Mary Helen Moves:

Marching Abs Sit on a mat with feet on floor. Lean back and position arms in front of you as if holding a beach ball. Lift right knee and turn upper body toward it. Lower foot and switch sides for 1 rep. Do 2 sets of 8 reps.

Anna Kaiser, AKT InMotion

Ashley Graham: "The first time I went to Anna's class, I felt like Beyoncé," says top model Ashley Graham (left), creator of the popular Net-a-Porter workout-video series Curvy Fit Club, shown with Kaiser.

Everything about Anna Kaiser's New York City studio, AKT InMotion, is hot. Red lightbulbs cast a dim glow over the spare industrial space. Foxes's "Body Talk" throbs over the sound system. The students, a mix of actresses, models and high-octane professional women, glisten with sweat. And, of course, there's Kaiser herself, a 5-foot-2 powerhouse in booty shorts and a black beanie, kicking, snaking and sashaying fiercely to the beat.

Kaiser specializes in helping women feel sexy in their own skin. The former professional dancer jets to Barcelona monthly to keep the ultimate hip shaker, singer Shakira, in tip-top shape. But wherever she is, Kaiser creates a vibe that's about letting loose and feeling free. "Anna is all woman," says AKT regular Sarah Siciliano Wragge, 33, a global marketing director at a production company in New York City. "She encourages us to let go."

Letting go in Kaiser's classes—they have playful names like AKTease, 4Play and S&M—means steamy dance moves plus strength intervals using resistance bands or weights. The first time, "you think you might die," jokes model and superfan Ashley Graham. Because Kaiser is generous with encouraging howls, she's not a big fan of breaks. "When you push yourself beyond what you thought you were capable of, you're powerful," Kaiser says. "You're your best self."

And for Wragge, her most confident self. "Anna has gotten me in touch with my sensuality," she says. "She's so empowered, it gives you permission to be the same." —Michelle Ruiz

Signature Anna Moves:

Hit It Stand with feet together. Step right with right foot, bending knees and leaning forward to tap floor with left hand. Stand, reaching right hand overhead and sliding feet together for 1 rep. Do 10 reps. Switch sides; repeat.

Pony Hop Stand on right foot, left leg crossed behind right, left arm extended overhead. Jump left onto left foot, bringing right leg behind left and extending right arm overhead for 1 rep. Do 20 reps.

Kick and Play Stand on left foot. Kick right foot forward, then jump out with legs wide, swinging hands at sides. Land with knees bent, hands on thighs. Repeat on opposite side for 1 rep. Do 10 reps.